The present demand for an increasingly rapid financial return in industrial plants such as smelting operations has driven operating parameters beyond their current performance limits. This has resulted in reduction in the lives of operating components of the plant, reduced operating efficiencies and reduction in product quality. The ever present need to reduce carbon and/or other greenhouse gas emissions is adding additional pressure to the situation. In the case of smelting operations, the control systems that are in use were implemented in the early 1980s whereas productivity, raw materials supply, energy price and environmental issues associated with the industry have intensified considerably since that time. Furthermore, the flexibility of pot line electricity usage is an increasingly important issue for smelters because of country and continental electricity grids and variation in availability and price which connection to such grids can impose.
Generally, control of processes has evolved in different ways depending on the type of system under consideration. The desire to maintain a process and its operating conditions at the optimum operating parameters for which it was designed, or subsequently retrofitted for the purpose of increased production and minimal capital investment, is a common requirement since these parameters determine the quality of the product and the efficiency and cost of the process. In an attempt to maintain operation at such optimum parameters, control systems have involved some form of compensatory control loop or feedback loop in order to maintain steady operating conditions for the industrial plant.
Thus, using a smelting operation as an example once again, a normal control strategy has fixed or specified operating targets for the key process variables associated with the smelting operation. These key variables are adjusted in a compensatory fashion using other control inputs. A problem with this approach is that this may produce greater variation over time and compound the initial causes of the variation. In fact, the initial causes of the variation may not be addressed at all due to the reliance on manipulation of control inputs not necessarily related to the cause, allowing the causes of the variation to remain embedded in the process and increase in number over time.
Further, in order to reduce complexity, assessment of the process condition in smelting cells has been characterised by a limited set of measurements performed, at different intervals, on each cell. The last data point for each routinely measured variable is usually the one used in assessment of cell state.
With the above arrangements, inadequate information is provided to enable comprehensive operational or automatic control of the smelting operation to be effected.